Dear Editor,
Nucleic acids are responsible for storing life’s “genetic code.” Decoding nucleic
acids enables scientists to understand the essence of life in depth. Anatomy is the
foundation of surgery; the secrets of surgery may lie in “natural spaces.” An excellent
surgeon is always following “avascular natural spaces.” Each finding of important
spaces is cheering for surgeons and will probably result in a leap in the development
of a series of operations. The membrane anatomy (MA) concept has been proposed against
this backdrop. It has been described as the “holy plane” and “angel hair” by Dr. Richard
J. Heald, who promotes the development of rectal cancer surgery.
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Significant progress has been made in gastrointestinal, rectal, and other surgeries
based on the “membrane plane,” which shows fewer surgical complications and a better
radical cure.
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Promisingly, the surgical era of MA is coming. However, the membrane–anatomy structures
are hard to display in cadaver dissection or surgical practice. Surgeries today are
still mainly based on gross anatomy from cadaver dissection and unsystematic “spaces”
found in operations, resulting in a high rate of complications and variation in surgical
quality.
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Demystifying human MA is thus of great importance.
What is the MA system? The MA is an anatomical system based on embryonic development.
Natural spaces between neighboring organs originate from different cell clusters growing
into different compartments with no cell mixing at boundaries.
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The fascia, called the “envelope,” surrounds the surface of each organ, and it is
expected to be the future unit of revised visceral anatomy.
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The organ’s intrinsic outlets, the blood or lymphatic vessels, and the nerve bundles
are the outlets of the “envelope.” Theoretically, each organ is covered with at least
two fascia layers, anteriorly and posteriorly, for example. These two layers appose
closely along the abdominal cavity when exceeding the contour of an organ. In cross-section,
the fascia looks like a circle. The intra-abdominal organs are all located between
the peritoneum and transversalis fascia, such as the digestive, urinary, and reproductive
systems. Each organ has its own “envelope”; several “envelopes” form concentric circles.
Natural spaces are found among these “envelopes.” The MA system consists of “envelopes,”
“outlets,” “natural spaces,” and then a conformation of “concentric circles.”
How can the MA system be verified and established? The Promethean fire of MA originates
in surgical practice. Despite efforts, the “envelope” is still just a surgical concept.
Conventional anatomical studies, such as cadaver dissection, microscopy, and imaging
examinations, have failed to validate the MA. Given the nature of MA, surgical practice
should be the most promising way to verify and establish the MA system. Nevertheless,
it takes work. First, a reliable criterion must be introduced to identify an actual
MA space. Second, surgeons in a particular field are usually only familiar with their
specialized anatomy; surgery for a specific organ usually involves only a few spaces.
Understanding the continuity of spaces needs overall cognition. Third, it is easy
to understand that space exists between the “envelopes,” but each “envelope” has several
“outlets,” which will break the continuity of the space. Fourth, as the pelvis is
characterized by a complicated morphology, its anatomy is controversial.
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Understanding the MA requires abstract thinking. Confirming and establishing the MA
system is thus challenging.
Every cloud has a silver lining. Since MA originates from embryonic development, we
can reconstruct the arrangement of “envelopes” according to organic development and
speculate on the potential “spaces” among them. We can then explore and validate these
“spaces” and “outlets” during surgery.
What will be the possible arrangement of pelvic organs based on their story of embryonic
development? The embryonic development of pelvic organs has been well understood.
We review this here. In the early embryonic period, the cloaca is the caudal outlet
of the visceral cavity. It is separated into two compartments by the urorectal septum
during the fourth to seventh weeks of development. The hindgut enters its posterior
compartment, which forms the future anal canal; the allantois enters its anterior
compartment, which forms the future urogenital sinus, where the excretory ducts of
the urogenital system enter. Specifically, the upper part of the urogenital sinus
gives rise to the urinary bladder, and its inferior narrow pelvic part gives rise
to the urethra. The caudal parts of the mesonephric ducts are absorbed into the bladder,
and the part of its outgrowth that is close to the cloaca entrance gives rise to the
ureteric buds and then forms the future ureters. In the middle of the second month,
the medial side of the mesonephros forms the urogenital ridge, where the gonad appears
initially. In males, with the shortening of the gubernaculum, the testes descend to
the scrotum. The gubernaculum also forms in females and forms the future round ligament.
The paramesonephric duct arises on the anterolateral surface of the urogenital ridge.
With the descent of the ovary, its cranial duct, which opens into the abdomen, develops
into the uterine tube. The caudal part, which runs laterally and then crosses ventrally
to the mesonephric duct and then contacts the urogenital sinus, fuses to form the
uterine canal and gives rise to the corpus and cervix of the uterus and the upper
portion of the vagina. (Figure 1A)
Figure 1
Diagram of embryonic development and characteristics of membrane anatomy under laparoscopy
(A) The schematic diagram of the embryonic development of pelvic organs.
(B) The right Latzko space under laparoscopy. It shows the characteristics of “envelope”
and “space”: smooth membrane planes on both sides, “angel hair” (indicated by the
yellow arrows) that should be pushed gently and bluntly, and the vascular network
(indicated by the red arrows) beneath the membrane.
Here, due to its proximity, we assign the gonad to the layer of the paramesonephric
duct. The arrangement of “envelopes” in the pelvis and lower abdomen, in a peritoneum-to-transversalis
fascia sequence, should thus ideally be as follows: peritoneum–digestive tract–gonad,
fallopian tube, uterus, and cervix; the upper segment of the vagina (paramesonephric
duct)–bladder, ureter, and kidney (mesonephric duct)–the layer of splanchnic nerves;
and main abdominal vessel–transversalis fascia. Each layer (i.e., “envelope”) continues
in the abdominopelvic cavity cranially and caudally. “Space” lies between “envelopes”
and continues as well, but the continuity is interrupted by the outlets of “envelopes.”
What are “envelope” and “space” characteristics under laparoscopy? A high-definition
laparoscopy presents characteristics of “angel hair” and “holy planes” perfectly in vivo.
After a great deal of careful surgical observation under laparoscopy, we conclude
that conforming the following three points indicates a proper way to enter the correct
space (Figure 1B) First, when entering a space, we can see the smooth membrane planes
on both sides. Second, note the vascular network beneath the membrane plane, which
can be seen clearly. Third, because different cell clusters grow into separate “envelopes”
with no cell mixing at boundaries, “spaces” naturally lie between “envelopes.” When
enlarging the space, it is practicable to push the “angel hair” gently and bluntly
rather than using the sharp dissection emphasized by Dr. Heald.
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These three points also comprise the criterion for intraoperatively judging the “envelope,”
that is, the natural boundary of an organ.
How can the “spaces” and “outlets” be explored and validated during laparoscopic surgery?
The reproductive system lies between the digestive and urinary systems. Radical surgery
for cervical cancer includes hysterectomy, paracolpium resection, and lymphadenectomy.
It involves almost all the “envelopes” in the pelvis. Verifying the abdominopelvic
MA in this surgery is thus possible. For better understanding, we drew a diagram based
on embryonic development and intraoperative findings, which shows the relationships
between the “envelopes,” the “outlets,” and the “spaces” (Figures 2A–2D). The intraoperative
characteristics of these “spaces” and “outlets” are also provided (Figures 2a–2j).
Figure 2
The “concentric circles” framework and surgical illustrations
(A–D) “Envelopes,” “spaces,” and “concentric circles” at four levels (the abdominal
aorta, common iliac vessels, cervix, and vagina plane, respectively). The circles
are interrupted by blood vessels (the outlets of an “envelope”), making the “spaces”
fragmented in C and D.
(a–j) “Spaces” and “outlets” during radical hysterectomy for cervical cancer (a-i)
and Burch suspension for stress urinary incontinence (j). The hole indicated by the
white arrows in (b) is the incision of the ureteral layer. The nerve layer (indicated
by the red arrow) runs laterally along the ureteral layer in (e). In (f), 1 represents
the vesical branch of the uterine artery, and 2 represents the superficial vesical
vein. The red arrow in (g) indicates the ureteral branch of the uterine artery.
AA, abdominal aorta; CIA, common iliac artery; CIV, common iliac vein; DUV, deep uterine
vein; EIA, external iliac artery; MVV, middle vesical vein; IIA, internal iliac artery;
IIV, internal iliac vein; IHP, inferior hypogastric plexus; IMA, inferior mesenteric
artery; IVC, inferior vena cava; IVV, inferior vesical vein; OA, ovarian artery; OV,
ovarian vein; Sig., sigmoid; SHP, superior hypogastric plexus; SUV, superficial uterine
vein; SVA, superior vesical artery; U, ureter; UA, uterine artery; UV, uterine vessels;
USL, uterosacral ligament; a., artery; l., ligament; s., space; v., vessel; n., nerve.
Here, we selected the common iliac and uterine vessels region for observation. Common
iliac vessels are at the true pelvis’s rim, where gynecological tumor surgeries usually
start. Structures here are relatively simple. In this region, the “envelope” of the
digestive tract (e.g., cecum, colon, and small intestine) is the innermost layer and
clings to the peritoneum. After incision of the peritoneum, we find that the “envelopes”
of ovarian vessels, ureters, and iliac vessels lie in a peritoneum-to-transversalis
fascia sequence with typical characteristics of MA (Figure 2B). At the level of the
abdominal aorta bifurcation, the neural layer of the superior hypogastric plexus travels
between the ureteral and aorta “envelopes” (Figure 2A). These “envelopes” can be pursued
into the pelvis and so can the “spaces” among them. The continuity of “envelopes”
can be easily understood, while the “outlets” make the “spaces” complicated.
In the uterine vessels region, the outlets of the uterus are uterine vessels, the
outlets of the urinary system are the vesicocervical ligament, and they form a cross
(Figure 2C). The uterine artery gives off a vesical branch and a ureteral branch;
the superficial vesical vein flows into the superficial uterine vein near the intramural
part of the ureter (Figure 2C). These vessels are located between the vesicovaginal
and lateral vesical space or between the Latzko space and the Okabayashi space near
the intramural part of the ureter (Figure 2C). These spaces are familiar for surgeons
specializing in radical hysterectomy.
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As an outlet of the vesical “envelope,” the middle and inferior vesical veins usually
flow into the deep uterine vein with a complex variation and are very close to the
vesical wall (Figure 2D). This means that there is traffic between the different outlets.
The outlets mentioned above and their traffic make the “space” fragmented.
When following into the pelvis, the space between the ureter and iliac vessels is
divided into the lateral vesical space and the Latzko space by uterine vessels and
is further divided into the Retzius and the lateral vesical space by the superior
vesical artery (outlet of the bladder) (Figures 2C and 2D). We also find that a neural
layer, the same layer as the superior hypogastric plexus, runs along the ureteral
layer laterally. These two layers are proximate here and are usually called by a joint
name, the mesoureter (Figures 2C and 2E). Furthermore, the space between the ureter
and ovarian vessels into the pelvis is divided into the Okabayashi and vesicovaginal
space by the outlets of the uterus (Figure 2C). Finally, the space between ovarian
vessels and the bowel is continuous with the uterosacral ligament’s medial and rectovaginal
space in the pelvis (Figure 2D).
To this end, the “concentric circles” framework is depicted entirely. Although folding
and curling occur in the embryonic stage, the arrangement of “envelopes” in a peritoneum-to-transversalis
fascia sequence is the same in the lower abdomen and the pelvis (Figures 2A–2D).
In this study, we introduced a proper way to enter the correct space and the criterion
for judging the natural boundary of an organ. Moreover, we may have sketched a rough
female MA map if MA is a surgical navigation system. It will probably redefine the
surgical scope of complete resections of pelvic tumors (cervical, rectal, and bladder
cancer), improve nerve-sparing and pelvic floor reconstruction, and reduce operative
bleeding and surgical injuries. It may positively affect surgical technique, oncological
results, and surgical training. We sincerely hope that in the future, more surgeons,
anatomists, and embryologists will verify this map, further revise and improve it,
and provide a better map for the upcoming era of MA surgery.